Known in the past has been a device for detecting a driver condition, such as inattention, using an image capturing means provided in a vehicle. For example, in the inattention judgment device described in PLT 1, the line of sight of the driver is detected from a facial image of the driver output by the image capturing means and, if the detected line of sight is outside a predetermined range, it is judged that the driver is looking aside. Further, when the vehicle is driving along a curve, the above predetermined range is changed by a predetermined amount in the direction of the curve.